1. Field of the Invention
The present invention relates generally to an apparatus and method for performing a handoff in a wireless communication system, and in particular, to an apparatus and method for performing a handoff using a mean of Received Signal Strengths (RSSs) subject to a downlink fast power control, in a wireless communication system.
2. Description of the Related Art
Wireless communication system supports a handoff technology for continually maintaining a call connection in order to guarantee mobility of a terminal in service, when the terminal moves from a serving cell to another serving cell. In other words, handoff is performed to maintain communication when the terminal moves between the cells. There have been proposed two handoff methods: one is soft handoff and another is hard handoff.
The soft handoff performs the service using channels allocated by a handoff target (or neighbor) Base Station (BS) and a serving BS together. After that, it releases the channel from the serving BS when a channel quality of the serving BS drops below a predetermined threshold. Alternatively, the hard handoff releases the channel from the serving BS and allocates a channel from a neighbor BS, when the channel quality of the serving BS drops below a predetermined threshold during a communication.
FIG. 1 is a flowchart illustrating a conventional method for performing a handoff in a wireless communication system. For example, a description will be made below on the basis of a hard handoff.
Referring to FIG. 1, in Step 101 a controller of the wireless communication system checks whether it receives a signal from a neighbor BS in communication with a serving BS.
In Step 103, upon the receipt of a signal from the neighbor BS, the controller measures the Received Signal Strength (RSS) (Pn) of a neighbor BS and the RSS (Pm) of the serving BS.
In Step 105, the controller compares the RSS (Pn) of the neighbor BS and the RSS (Pm) of the serving BS with a preset threshold (Pth), to determine whether to perform the hard handoff. The controller returns to the Step 101, and checks whether it receives a signal from the neighbor BS, when the RSS (Pn) of the neighbor BS is less than the threshold (Pth) (i.e., Pn<Pth) or the RSS (Pm) of the serving BS is greater than or equal to the threshold (Pth) (i.e., Pm≧Pth).
In Step 107, the controller performs the hard handoff to the neighbor BS. Next, the controller terminates the algorithm.
As described above, the hard handoff is performed in the wireless communication system, when the RSS of the serving BS is less than the threshold and the RSS of the neighbor BS is greater than or equal to the threshold. Thus, the hard handoff has a drawback that a ping-pong phenomenon occurs and call quality is deteriorated, when the RSS of the neighbor BS is greater than or equal to the threshold in a handoff area.